1. Field of the Invention
The present invention relates generally to presentation projectors for projecting computer generated presentations and other images to a viewing surface. In particular, the present invention relates to technology that enables the wireless transmission of an image to a presentation projector.
2. Background Information
The widespread acceptance of using computers to facilitate group communications has created a large demand for devices that project computer displays. As a result, corporate enterprises have installed multimedia projection systems in many workplace conference rooms, or provide access to portable presentation equipment that can be used in conference rooms as needed. In a typical operating mode, multimedia projection systems receive analog video signals from a personal computer (“PC”). The video signals may represent still, partial, or full-motion display images of a type rendered by the PC. The analog video signals are typically converted in the projection system into digital video signals, and the signals are electronically conditioned and processed to control an image-forming device, such as a liquid crystal display (“LCD”) or a digital micro-mirror device (“DMD”).
A popular type of multimedia projection system employs a broad-spectrum light source and optical path components upstream and downstream of the image-forming device to project the image onto a display screen. An example of a DMD-based multimedia projector is the model LP420 manufactured by InFocus Corporation., of Wilsonville, Oreg., the assignee of the present application.
To display their presentations, users tote portable computers such as laptops into the conference room, and attach the computer to the projector using a connecting cable. The necessity of carrying heavy cabling to attach the computer to the projector is inconvenient, especially when giving mobile presentations. Issues of cable compatibility or malfunction may occur and the set-up time is increased. Moreover, if more than one presenter uses the projection equipment, each with their own laptops, then each successive presenter needs to repeat the cabling set-up procedure, which results in a delay between presentations.
One way to eliminate the cabling problem is to transmit the image over a wireless communications link instead of a cable connection. Wireless transmission of an image to a projector is known in the art. For example, U.S. patent. application Ser. No. 5,847,748, Multimedia Projection System, which issued on Dec. 8, 1998, to David P. Laughlin, (the “'748 patent”) discloses a multimedia projection system that includes a notebook computer that has an integral projector. The projector described in the '748 patent is capable of receiving information from the computer's central processing unit through a cable or a wireless communication circuit, including an infrared communication circuit.
An example of a prior art wireless presentation projector is the Notevision5 Liquid Crystal Display (LCD) projector manufactured by the Sharp Electronics Corporation of Mahwah, N.J. The Notevision5 LCD projector features an infrared communication capability, which allows users to transfer digital images from a laptop or a compatible device directly to the projector. The Sharp Notevision5 LCD projector relies on an Infrared Data Association (IrDA) data communication standard to transmit the image from the computer to the projector. One of the drawbacks to using the IrDA data communication standard is the bandwidth limitation inherent in infrared communications. Transmission data rates are low, with a maximum data transmission speed of up to 4 Mb/s (megabytes per second). This results in a very slow image update, typically up to at least 15 seconds per screen. The slow image update rate is unacceptable to most presentation system users.
In an effort to overcome the low data transmission rates, the IrDA data communication standards provide for converting and storing images in a compressed format in order to reduce the amount of data that is transmitted. The Sharp Notevision5 projector uses the Joint Photographic Experts Group (JPEG) image compression format, which is documented by the International Organization for Standards (ISO) in ISO standard 10918, Information technology—Digital compression and coding of continuous-tone still images, first published in 1994. However, the conversion and storage of the image using the JPEG image compression format is a process that is computationally intensive and necessarily delays the transmission of the image from the computer to the projector. Moreover, the size of the compressed JPEG images of a typical presentation is still unacceptably large, which does not allow for satisfactory update rates for displaying a wireless projected image.
Yet another drawback inherent in the use of the IrDA data communication standard is that infrared communication is a short-range technology limited to about a 30–50 foot radius. In addition, infrared communication is highly directional because the infrared signals cannot penetrate solid objects. Thus, interference is common and the signals can even be affected by indoor lighting (e.g. the use of fluorescent lights) and air quality (e.g. the presence of dust or smoke).
What is needed, therefore, is an improved method of wireless image transmission between a computer and a projector. In particular, the wireless transmission of an image that is independent of the wireless transmission medium and that provides for faster updates of the projected image in an efficient and user-friendly way presents a unique set of challenges, requiring a new and novel solution.